The Federal Competition Commission said Telmex refused to give rival firm Axtel access to landlines in 32 towns from August 2009 to June 2011, blocking Axtel from providing local and long-distance services.

"For this reason, the CFC found that the refusal constitutes a monopolistic practice," the agency said in a statement.

Slim, considered the world's richest man, dominates the telecom market in Mexico. Telmex, a former state monopoly privatized in 1990, holds around 80 percent of the fixed-line market.